1. Field of the Invention
The present invention relates to a rotatable head type digital recording and reproducing device having a plurality of operation modes, and more particularly, to a magnetic recording and reproducing device for recording and reproducing data signals with different tape feeding speeds respectively.
2. Description of the Prior Art
FIG. 1 shows a block diagram of a conventional magnetic recording and reproducing device. Analog signals to be recorded which are entered from an input terminal 1 are applied to a record signal processing unit 2, wherein the analog signals are converted into digital signals. Added to the converted digital record signals are one or more synchronizing bits and parity bits, thereby converting the digital record signals into an array of digital signals in a predetermined recording format. The converted digital signal array as mentioned above is modulated into high frequency signals having a frequency appropriate for recording on a magnetic tape 4, such as a frequency f.sub.0 for a logic "0" bit and a frequency f.sub.1 for a logic "1" bit. Subsequently, the modulated high frequency signals entered amplifiers 5a and 5b.
The modulated signals entering the amplifiers 5a and 5b are current amplified and outputted to coils A1 and B1, respectively, which are provided in a fixed drum SD. Coils A2 and B2 which are provided in a rotary drum RD are magnetically coupled to the coils A1 and B1 respectively so as to constitute rotary transformers. The output signals of the amplifiers 5a and 5b which are frequency modulated are transmitted to the coils A2 and B2 through the coils A1 and B1 by induction and are recorded on the magnetic tape 4 through magnetic heads A and B respectively.
The magnetic heads A and B are disposed on the rotary drum RD so as to oppose each other at an angle of 180.degree. as shown in FIG. 2. When the magnetic head A or B traces a track on the magnetic tape 4 to detect a signal and if one of the magnetic heads A and B comes in contact with an adjacent track, cross talk occurs with the adjacent track, resulting in noise occurring in the reproduced signals. Therefore, the magnetic heads A and B are attached to the drum RD with different azimuth angles to reduce the cross talk. For example, the magnetic head A is attached to the rotary drum RD having with an azimuth angle of plus 20.degree. and the magnetic head B is attached to the rotary drum RD having an opposite azimuth angle of minus 20.degree.. Above "azimuth angle" means an inclination angle between a line perpendicular to the track and a head gap. The azimuth angle is defined to reduce the cross talk between two adjacent tracks.
As shown in FIG. 2, the magnetic tape 4 is wound along the circumference surface of the rotary drum RD for about 90.degree. and the feeding direction of the magnetic tape 4 is coincident with the rotating direction of the rotary drum RD.
FIG. 3 shows a track pattern recorded on the magnetic tape 4, wherein tracks a.sub.1, a.sub.2, ..., a.sub.5, ... (represented as "a" hereinafter) are the tracks recorded by the magnetic head A and tracks b.sub.1, b.sub.2, ..., b.sub.4, ... (represented as "b" hereinafter) are the tracks recorded by the magnetic head B. The signals recorded in the track patterns a and b as shown in FIG. 3 are reproduced through the magnetic heads A and B provided on the rotary drum RD. When the head gap of the magnetic head A traces along the track a.sub.1 e.g. shown in FIG. 3, the magnetic lines of force of the head gap of the magnetic head A are varied in response to the record signals. The variation in the magnetic lines of force thereof is transmitted to the coil A1 provided in the fixed drum SD, wherein the coil A1 is magnetically coupled with the coil A2 provided in the rotary drum RD, thereby varying the induced voltage in the coil A1. Also, the recorded signals on the track b1 are similarly transmitted to the coil B1 as the induced voltage variation.
The reproduced signals output from the coils A1 and B1 are respectively applied to amplifiers 6a and 6b through a signal selecting switch 7. The reproduced signals are not continuous signals but intermittent signals generated from the coils A1 and B1 every time during which the magnetic heads A or B trace any one of the tracks on the magnetic tape 4 as shown in FIG. 2. Accordingly, one of the amplifier 6a or 6b is selected by switching the signal selecting switch 7 in response to a switching signal sent from a reproduction signal processing unit 10 so as to transmit the reproduced signal from the magnetic head A or B which is tracing the track and reproducing the signal. Both of the reproduced signals sent from the coils A1 and B1 are applied to equalizers, 8a and 8b. The equalizer 8a is selected when the rotational speed of the rotary drum RD is e.g. 2000 r.p.m., and the equalizer 8b is selected when the rotational speed of the rotary drum RD is e.g. 1000 r.p.m.. An equalizer selection switch 9 is switched in response to a recording time selection signal which is entered from an input terminal 3.
If the rotational speed of the rotary drum RD is different, the property of the magnetic head is different depending on the frequency of the reproduced signal. Therefore, any one of the equalizers 8a and 8b is selected corresponding to the rotational speed of the rotary drum RD so as to recover the frequency property and the phase property of the reproduced signals sent from the coils A1 and B1.
FIG. 4 shows timing charts of an input signal of the reproduction signal processing unit 10, wherein FIG. 4(1) is a timing chart in a period when the rotational speed of the rotary drum RD is 2,000 r.p.m. and the feeding speed of the magnetic tape 4 is 8.15 mm/sec., for a normal recording and reproducing operation, and FIG. 4(2) is a timing chart in a period when the rotational speed of the rotary drum RD is 1,000 r.p.m., and the feeding speed of the magnetic tape 4 is 4.075 mm/sec., for a long time recording and reproducing operation. In FIG. 4(1), the time a.sub.1 represents the time for reproducing the signal recorded on the track a.sub.1 sent through the magnetic head A, and also the time b.sub.1 represents the time for reproducing the signal recorded on the track b.sub.1 through the magnetic head B. In FIG. 4(2), since the feeding speed of the magnetic tape 4 is half the tape feeding speed of the situation shown in FIG. 4(1), it takes twice of the recording or reproducing time of the situation shown in FIG. 4(1) for recording and reproducing the signal through each of the heads in the situation of FIG. 4(2).
The reproduction signal processing unit 10 demodulates the output signals of the equalizer 8a or 8b selected by the equalizer selection switch 9 to the digital signal array so as to obtain digital signals synchronized with the synchronizing bit. After errors in the digital signals are corrected with reference to the parity bit, digital reproduced signals are obtained. The obtained digital reproduced signals are converted to analog signals, whereby the reproduced analog signals are outputted from the output terminal 11.
In the conventional digital magnetic recording device as described above, since the rotation speed of the rotary drum RD is different between the normal recording and reproducing operation and the long time recording and reproducing operation, it is necessary to provide two sets of the reproduction equalizer unit, therefore the size of the magnetic recording and reproducing device has become large.